Speed control device

ABSTRACT

In a speed control system, there are provided a speed observer compensator ( 10 ) for inputting a difference between a speed V M  of a mechanical system ( 5 ) and an estimated value V MO  of a speed of the mechanical system ( 5 ) which is obtained by a speed observer ( 6 ) and outputting a speed difference V M −V MO  based on the input, and a mechanical system model ( 8 ) for inputting a sum of an output of the speed observer compensator ( 10 ) and an output T ro  of a PI controller ( 2 ), and the speed observer ( 6 ) is constituted in such a manner that the signal V MO  produced after a passage of an output of the mechanical system model ( 8 ) through a filter delay element model ( 11 ) and a dead time delay element model ( 12 ) is equal to the speed V M  of the mechanical system ( 5 ), and the output of the mechanical system model ( 8 ) is set to be a speed feedback signal V f  of the speed control system. Consequently, it is possible to provide a speed control device capable of removing the high frequency component of the speed feedback signal, compensating for the phase delay of the delay element so as not to generate an oscillation having a high frequency, and causing the speed of the mechanical system to follow a target speed with high precision.

TECHNICAL FIELD

[0001] The present invention relates to a speed control device capableof constituting a speed observer including the delay element of acontrol system and setting the estimated value of a non-delayed speed ofthe speed observer to be a speed feedback signal, thereby removing thehigh frequency component of the speed feedback signal and increasing theresponse performance of the control system by one stage.

BACKGROUND ART

[0002] In general, a speed control system in which a filter delayelement or a dead time delay element is present in a controller or acontrol object is shown in FIG. 3. FIG. 3 is a block diagram showing ageneral speed control system.

[0003] In FIG. 3, 1 denotes a subtractor, 2 denotes a PI controller, 3denotes a filter delay element, 4 denotes a dead time delay element, 5denotes a mechanical system including a motor, V_(r) denotes a targetspeed, V_(f) denotes a speed feedback signal, and V_(M) denotes a speed.

[0004] In a general speed control device, both a speed signal obtainedfrom a speed sensor (not shown) and a speed signal obtained bydifferentiating a position signal of a position sensor (not shown) havehigh frequency ripple components. Also in the control system shown inFIG. 3, therefore, the speed feedback signal V_(f) has the highfrequency ripple component, and furthermore, the phase of the filterdelay element 3 or the dead time delay element 4 is delayed. For thisreason, there is a problem in that the gain of the PI controller 2 isnot increased and a sufficient response characteristic cannot beobtained. In order to improve such a problem of controllability, thefollowing conventional art has been proposed.

[0005]FIG. 4 is a block diagram showing a control system according to afirst conventional art. The same components in the first conventionalart as those in FIG. 3 have the same reference numerals and descriptionwill be omitted, and only different components will be described. InFIG. 4, 7 denotes an adder, 8 denotes a model of a mechanical systemincluding a motor, 9 denotes a subtractor, 10 denotes a speed observercompensator, and 14 denotes a speed observer. As shown in FIG. 4, anobserver of the mechanical system is constituted and a speed estimatedvalue of the smooth observer is set to be a speed feedback signal V_(f).Consequently, a torque waveform is not disturbed so that the gain of thePI controller 2 can be increased (for example, JP-A-11-136983).

[0006] Moreover, FIG. 5 is a block diagram showing a control systemaccording to a second conventional art. Components in the secondconventional art are different from those in FIG. 3 in that a phaseleading compensator 13 is added in series to a control system. In thephase leading compensator 13, if T_(a) and T_(b) are properly set to beT_(a)>T_(b), the phase of the phase leading compensator 13 is led.Consequently, the gain of the PI controller 2 can be increased, andfurthermore, a control performance can be enhanced.

[0007] In the first conventional art, however, the high frequencycomponent of the speed feedback signal V_(f) is removed and a problem ofthe phase delay of a control loop is not solved at all. For this reason,there is a problem in that the gain of the PI controller 2 cannot beincreased sufficiently.

[0008] In the second conventional art, moreover, a gain in the highfrequency area of the phase leading compensator 13 is increased.Consequently, there is a problem in that an oscillation having a highfrequency is apt to be caused.

[0009] In order to solve the problems, it is an object of the inventionto provide a speed control device capable of removing the high frequencycomponent of a speed feedback signal, compensating for the phase delayof a delay element so as not to generate an oscillation having a highfrequency, and causing the speed of a mechanical system to follow atarget speed with high precision.

DISCLOSURE OF THE INVENTION

[0010] In order to solve the problems, the invention provides a speedcontrol device to be a speed control system in which a filter delayelement (3) or a dead time delay element (4) is present in a controlleror a control object and a PI control is carried out to follow a speedcommand to be a target speed V_(r), comprising a speed observercompensator (10) for inputting a difference between a speed V_(M) of amechanical system (5) and an estimated value V_(MO) of a speed of themechanical system (5) which is obtained by a speed observer (6) andoutputting a speed difference V_(M)−V_(MO) based on the input, and amechanical system model (8) for inputting a sum of an output of thespeed observer compensator (10) and an output T_(ro) of a PI controller(2), wherein the speed observer (6) is constituted in such a manner thatthe signal V_(MO) produced after a passage of an output of themechanical system model (8) through a filter delay element model (11)and a dead time delay element model (12) is equal to the speed V_(M) ofthe mechanical system (5), and the output of the mechanical system model(8) is set to be a speed feedback signal V_(f) of the speed controlsystem.

DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is a block diagram illustrating the principle of thestructure of a control system according to an embodiment of theinvention.

[0012]FIG. 2 is an equivalent block diagram in FIG. 1.

[0013]FIG. 3 is a block diagram showing an ordinary feedback controlsystem.

[0014]FIG. 4 is a block diagram showing a control system according to afirst conventional art.

[0015]FIG. 5 is a block diagram showing a control system according to asecond conventional art.

MODE OF CARRYING OUT THE INVENTION

[0016] An embodiment of the invention will be described with referenceto the drawings.

[0017]FIG. 1 is a block diagram showing the principle of the structureof a control system according to the embodiment of the invention. Thesame components of the invention as those of the conventional art havethe same reference numerals and description will be omitted, and onlydifferent components will be described.

[0018] In FIG. 1, 11 denotes a filter delay element model, 12 denotes adead time delay element model, and 6 denotes a speed observer.

[0019] The invention is different from the conventional art as follows.

[0020] More specifically, in a speed control system in which a filterdelay element 3 or a dead time delay element 4 is present in acontroller or a control object and a PI control is carried out to followa speed command to be a target speed V_(r), comprising a speed observercompensator 10 for inputting a difference between a speed V_(M) of amechanical system 5 and an estimated value V_(MO) of a speed of themechanical system 5 which is obtained by a speed observer 6 andoutputting a speed difference V_(M)−V_(MO) based on the input, and amechanical system model 8 for inputting a sum of an output of the speedobserver compensator 10 and an output T_(ro) of a PI controller 2, thespeed observer 6 is constituted in such a manner that the signal V_(MO)produced after a passage of an output of the mechanical system model 8through a filter delay element model 11 and a dead time delay elementmodel 12 is equal to the speed V_(M)of the mechanical system 5, and theoutput of the mechanical system model 8 is set to be a speed feedbacksignal V_(f) of the speed control system.

[0021] Next, an operation will be described.

[0022] In FIG. 1, the output T_(ro) of the PI controller 2 and theoutput of the speed observer compensator 10 are added and input to themechanical system model 8 (including a motor). The output of themechanical system model 8 (including the motor) is set to be the speedfeedback signal V_(f) of the control system, and a signal obtained bysubtracting the speed feedback signal V_(f) from the target speed V_(r)is input to the PI controller 2 and the output T_(ro) of the PIcontroller 2 is input to the mechanical system (including the motor)through the filter delay element 3 and the dead time delay element 4 tocontrol the mechanical system (including the motor), while the sameoutput is input to a subtractor 9 through the filter delay element model11 and the dead time delay element model 12 and is then subtracted fromthe speed V_(M) of the mechanical system (including the motor), and asignal thus obtained is input to the speed observer compensator 10.

[0023] Referring to FIG. 1, in an open loop, a transfer function fromthe output T_(ro) of the PI controller 2 to the speed feedback signalV_(f) is expressed in the following Equation (1). $\begin{matrix}{\frac{V_{f}(s)}{T_{r\quad 0}(s)} = \frac{1}{{Js} + D}} & {{Eq}.\quad (1)}\end{matrix}$

[0024] If the closed loop of the speed observer is stable, therefore,the control system in FIG. 1 can be rewritten equivalently as shown inFIG. 2. FIG. 2 is an equivalent block diagram in FIG. 1. Referring toFIG. 2, the stability of a feedback control system is the same as thatof a system having no delay. Even if the gain of the PI controller isincreased greatly, the control system can be prevented from beingunstable. Moreover, a transfer function from the target speed V_(r) tothe speed V_(M) of the mechanical system is expressed in the followingEquation (2). $\begin{matrix}{\frac{V_{M}(s)}{V_{r}(s)} = {{\frac{{K_{p}s} + K_{i}}{{Js}^{2} + {\left( {D + K_{p}} \right)s} + K_{i}} \cdot \frac{1}{1 + {T_{f}s}}}^{{- T_{d}}s}}} & {{Eq}.\quad (2)}\end{matrix}$

[0025] Thus, it is possible to cause the speed V_(M) of the mechanicalsystem to follow the target speed V_(r) with high precision byincreasing gains K_(p) and K_(i) of the PI controller 2. Moreover, theloop of the speed observer has a delay element and an input/outputcharacteristic is not related to a compensator C_(o) (s) of the speedobserver based on the Equation (2). Therefore, the gain of thecompensator C_(o) (s) of the speed observer may be set to be small.Accordingly, a stable speed observer can be constituted easily.

[0026] Therefore, the invention provides the speed control system inwhich the filter delay element 3 or the dead time delay element 4 ispresent in a controller or a control object and a PI control is carriedout to follow a speed command to be the target speed V_(r), comprisingthe speed observer compensator 10 for inputting a difference between thespeed V_(M) of the mechanical system 5 and the estimated value V_(MO) ofa speed of the mechanical system 5 which is obtained by the speedobserver 6 and outputting the speed difference V_(M)−V_(MO) based on theinput, and the mechanical system model 8 for inputting a sum of anoutput of the speed observer compensator 10 and the output T_(ro) of thePI controller 2, wherein the speed observer 6 is constituted in such amanner that the signal V_(MO) produced after a passage of an output ofthe mechanical system model 8 through the filter delay element model 11and the dead time delay element model 12 is equal to the speed V_(M) ofthe mechanical system 5, and the output of the mechanical system model 8is set to be the speed feedback signal V_(f) of the speed controlsystem. Therefore, the speed observer including the delay element of thecontrol system is constituted and the estimated value of a non-delayedspeed of the speed observer is set to be the speed feedback signal.Consequently, the high frequency component of the speed feedback signalcan be removed.

[0027] Moreover, the control system is divided into a feedback controlsection and a speed observer section. Consequently, the stability of thefeedback loop is the same as that of a system having no delay so thatthe gain of the PI controller can be increased greatly. Thus, theresponse performance of the control system can be enhanced by one stage.

[0028] Although the loop of the speed observer has the delay element,furthermore, the compensator of the speed observer does not influencethe input/output characteristic. Therefore, the gain of the compensatorof the observer may be set to be small. Consequently, the stableobserver can be constituted easily. More specifically, the highfrequency component of the speed feedback signal is removed and thephase delay of the delay element is compensated so as not to cause anoscillation having a high frequency. Therefore, the gain of the PIcontroller can be increased and the speed of the mechanical system canbe caused to follow the target speed with high precision.

Industrial Applicability

[0029] As described above, the speed control device according to theinvention is useful to be utilized for a speed control device of anelectric motor in which a filter delay element or a dead time delayelement is present in a controller or a control object.

1. A speed control device to be a speed control system in which a filterdelay element (3) or a dead time delay element (4) is present in acontroller thereof or a control object thereof and a PI control iscarried out to follow a speed command to be a target speed V_(r),comprising a speed observer compensator (10) for inputting a differencebetween a speed V_(M) of a mechanical system (5) and an estimated valueV_(MO) of a speed of the mechanical system (5) which is obtained by aspeed observer (6) and outputting a speed difference V_(M)−V_(MO) basedon the input thereof, and a mechanical system model (8) for inputting asum of an output of the speed observer compensator (10) and an outputT_(ro) of a PI controller (2), wherein the speed observer (6) isconstituted in such a manner that the signal V_(MO) produced after apassage of an output of the mechanical system model (8) through a filterdelay element model (11) and a dead time delay element model (12) isequal to the speed V_(M) of the mechanical system (5), and the output ofthe mechanical system model (8) is set to be a speed feedback signalV_(f) of the speed control system.